b)
Expand the equation: \begin{align} ∑F_y &\cssId{Step1}{=0}\\[3px] &\cssId{Step2}{FA_y-1/2·m·g+F_By}\\[3px] &\cssId{Step3}{F_A -\frac{1}{2}·m·g + F_B = 0}\\[3px] &\cssId{Step4}{F_B= \frac{1}{2}·m·g - F_A }\\[3px] &\cssId{Step5}{F_B= }\\[3px] \end{align}